1. Field of the Invention
One embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. One embodiment of the invention disclosed in this specification and the like also relates to a process, a machine, manufacture, or a composition of matter. In particular, one embodiment of the invention disclosed in this specification and the like relates to a semiconductor device, or an electronic device including a semiconductor device.
In this specification and the like, the term “semiconductor device” denotes a device that can function by utilizing semiconductor characteristics. A display device (e.g., a liquid crystal display device and a light-emitting display device), a lighting device, an electro-optical device, a power storage device, a memory device, a semiconductor circuit, an imaging device, an electronic device, and the like may include a semiconductor device.
2. Description of the Related Art
In recent years, transistors including an oxide semiconductor in a semiconductor layer where a channel is formed (hereinafter referred to as an “OS transistor”) have garnered attention. An oxide semiconductor layer can be formed by a sputtering method or the like, and thus can be used for a semiconductor layer of a transistor in a large display device, for example. In addition, OS transistors can be fabricated by improving parts of a production equipment for transistors including amorphous silicon in a semiconductor layer where a channel is formed; this can reduce the capital investment.
It is known that an OS transistor has an extremely low leakage current in an off state. For example, a low-power CPU and the like utilizing the extremely low leakage current of an OS transistor have been disclosed (see Patent Document 1).